Project Summary/Abstract Multiple Myeloma (MM) is the second most common form of blood cancer and remains an incurable and deadly disease. Proteasome inhibitor (PI) therapy is a cornerstone in the treatment of MM, but resistance to this class of agent is an emerging challenge in the clinic. New therapeutic approaches that specifically target resistance are needed to maximize responses and ultimately produce cures. We have identified a hit-stage drug, compound E61, that selectively kills MM cells over normal cells, restores the activity of PIs in resistant MM cells, and cures more that 1/3 of mice with MM without any signs of toxicity. We have designed new derivatives of E61 that have optimized pharmaceutical properties. The specific goals of the proposed project are (1) to conclusively demonstrate increased metabolic stability and anti-MM activity of optimized E61 derivatives, and (2) to show superior in vivo activity of optimized derivatives using a mouse model of MM. Compounds will be tested as single agents and in combination with FDA-approved PIs. These study aims are based on strong preliminary medicinal chemistry work that identified structure activity relationships (SAR) of compound E61. This information has enabled the strategic design of the derivatives that we will test in the proposed study. The proposed experiments capitalize on industry standard assay systems for measuring pharmacological properties of new drugs in vitro, including metabolic stability in blood plasma and liver microsomes, and assays directly measuring drug metabolism by the catechol-O-methyltransferase (COMT) enzyme. In vitro assays for measuring anti-MM activity and predicting toxicity include the use of panels of genetically diverse PI sensitive and resistant MM cells and a variety of normal blood and fibroblast cell types. For evaluating the performance of novel derivatives in vivo we will use an established model of experimentally induced MM that accurately recapitulates the human MM pathology in NOD-SCID IL2Rgammanull (NSG) mice. Through the use of these tools, and predictions based on a breadth of preliminary data, it is our expectation that this work will deliver a promising new compound for the treatment of refractory MM.